.\"	$OpenBSD: SSL_CTX_set_max_cert_list.3,v 1.6 2019/06/12 09:36:30 schwarze Exp $
.\"	OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100
.\"
.\" This file was written by Lutz Jaenicke <jaenicke@openssl.org>.
.\" Copyright (c) 2001 The OpenSSL Project.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\"
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\"
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in
.\"    the documentation and/or other materials provided with the
.\"    distribution.
.\"
.\" 3. All advertising materials mentioning features or use of this
.\"    software must display the following acknowledgment:
.\"    "This product includes software developed by the OpenSSL Project
.\"    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
.\"
.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
.\"    endorse or promote products derived from this software without
.\"    prior written permission. For written permission, please contact
.\"    openssl-core@openssl.org.
.\"
.\" 5. Products derived from this software may not be called "OpenSSL"
.\"    nor may "OpenSSL" appear in their names without prior written
.\"    permission of the OpenSSL Project.
.\"
.\" 6. Redistributions of any form whatsoever must retain the following
.\"    acknowledgment:
.\"    "This product includes software developed by the OpenSSL Project
.\"    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
.\" OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd $Mdocdate: June 12 2019 $
.Dt SSL_CTX_SET_MAX_CERT_LIST 3
.Os
.Sh NAME
.Nm SSL_CTX_set_max_cert_list ,
.Nm SSL_CTX_get_max_cert_list ,
.Nm SSL_set_max_cert_list ,
.Nm SSL_get_max_cert_list
.Nd manipulate allowed size for the peer's certificate chain
.Sh SYNOPSIS
.In openssl/ssl.h
.Ft long
.Fn SSL_CTX_set_max_cert_list "SSL_CTX *ctx" "long size"
.Ft long
.Fn SSL_CTX_get_max_cert_list "SSL_CTX *ctx"
.Ft long
.Fn SSL_set_max_cert_list "SSL *ssl" "long size"
.Ft long
.Fn SSL_get_max_cert_list "SSL *ctx"
.Sh DESCRIPTION
.Fn SSL_CTX_set_max_cert_list
sets the maximum size allowed for the peer's certificate chain for all
.Vt SSL
objects created from
.Fa ctx
to be
.Fa size
bytes.
The
.Vt SSL
objects inherit the setting valid for
.Fa ctx
at the time
.Xr SSL_new 3
is being called.
.Pp
.Fn SSL_CTX_get_max_cert_list
returns the currently set maximum size for
.Fa ctx .
.Pp
.Fn SSL_set_max_cert_list
sets the maximum size allowed for the peer's certificate chain for
.Fa ssl
to be
.Fa size
bytes.
This setting stays valid until a new value is set.
.Pp
.Fn SSL_get_max_cert_list
returns the currently set maximum size for
.Fa ssl .
.Pp
During the handshake process, the peer may send a certificate chain.
The TLS/SSL standard does not give any maximum size of the certificate chain.
The OpenSSL library handles incoming data by a dynamically allocated buffer.
In order to prevent this buffer from growing without bound due to data
received from a faulty or malicious peer, a maximum size for the certificate
chain is set.
.Pp
The default value for the maximum certificate chain size is 100kB (30kB
on the 16bit DOS platform).
This should be sufficient for usual certificate chains
(OpenSSL's default maximum chain length is 10, see
.Xr SSL_CTX_set_verify 3 ,
and certificates without special extensions have a typical size of 1-2kB).
.Pp
For special applications it can be necessary to extend the maximum certificate
chain size allowed to be sent by the peer.
See for example the work on
.%T "Internet X.509 Public Key Infrastructure Proxy Certificate Profile"
and
.%T "TLS Delegation Protocol"
at
.Lk https://www.ietf.org/
and
.Lk http://www.globus.org/ .
.Pp
Under normal conditions it should never be necessary to set a value smaller
than the default, as the buffer is handled dynamically and only uses the
memory actually required by the data sent by the peer.
.Pp
If the maximum certificate chain size allowed is exceeded, the handshake will
fail with a
.Dv SSL_R_EXCESSIVE_MESSAGE_SIZE
error.
.Sh RETURN VALUES
.Fn SSL_CTX_set_max_cert_list
and
.Fn SSL_set_max_cert_list
return the previously set value.
.Pp
.Fn SSL_CTX_get_max_cert_list
and
.Fn SSL_get_max_cert_list
return the currently set value.
.Sh SEE ALSO
.Xr ssl 3 ,
.Xr SSL_CTX_ctrl 3 ,
.Xr SSL_CTX_set_verify 3 ,
.Xr SSL_new 3
.Sh HISTORY
These functions first appeared in OpenSSL 0.9.7
and have been available since
.Ox 3.2 .
